OK, so this morning I woke at 5 a.m., didn't go back to sleep, so finally got up at 6:20, fed the horses and barn cats, and then took a flashlight and checked the ponds. I found only 2 fish laying on their sides, and not all the way sideways, just leaning over. The others are all swimming. Go figure! The 3 fantails were all spotted and swimming normally. I think of them as being more fragile than the larger goldfish. Both koi are fine, too. I wanted to confirm in my mind how many leaves were in there, and there are 2 areas about 3' diameter where there is a "bed" of leaves that are probably loosely laying 3" deep. If they sunk down and compacted, it would be less than 1" of leaf matter. Same with koi pond, nearly none in there though. So, leaving the leaves for the fish and frogs to snuggle into. And, the fact that I only saw a couple of the fish laying more sideways, I'm not going to worry. I suspect it has to do with the chemical in the water in the koi pond, that overflowed into the goldfish pond, as that is when I noticed them turn sideways, and was also when we went from very warm to very cold in 24 hours. So, I'm back to assuming there was still residual chemicals in the koi pond from August fungicide spraying, that overflowed and contaminated the goldfish pond ... again. I can't do much of a water change to the koi pond this time of year, but going to drain it down a few inches and refill it this evening, to help it out a little. All the koi are swimming normally, finally was able to spot them, as almost all ice is gone. I think all will be fine. I have ponds running as I do in summer, nothing extra right now. Will be shutting down the skippy and fountain when the next cold snap hits, though, so as not to worry about ice jambs on the waterfall, and also to not chill the water more, although that's the koi pond. Stream will continue to flow in the goldfish pond, as I ran that all last winter with no issues, as well as the bog in that pond. Only aerator will be running in the koi pond when it gets to teens in a couple of days.